1. Technical Field
The present disclosure pertains to a removable wafer expander for die bonding equipment.
2. Description of the Related Art
In the assembly of semiconductor devices, a wafer is mounted onto a flexible sticky foil held by a metal ring. After wafer sawing for singularizing the dies within each wafer, every individual die has to be picked from the sticky foil and placed directly on a substrate over a die attach material (package).
Thus is provided pick-and-place equipment with a die ejector system that pushes the die back side to break the adhesion forces of the sticky foil. A vacuum pick-up tool (robotic arm) picks the die and through coordinated motion places the picked die over the targeted placement position.
Critical parameters for the pick-up process are the die back side adhesion to the sticky foil and the separation between each die. The latter is mainly governed by the “wafer street width” and consequently by the cutting blade thickness.
The market trend is to continuously reduce the die size, maximizing the number of dies per wafer. Thus, stretching the sawn wafer to uniformly enlarging the separation between each die is an option to be considered to optimize the die pick-up process.
The deformation of the sticky foil happens on the die bonding equipment, and the expansion is not suddenly recovered on releasing the wafer expander from the die bonding equipment. In some cases a permanent deformation occurs; therefore, it is not possible to use the wafer anymore.
Thus, it is highly advisable that the wafer remains expanded by the wafer expander of the die bonding equipment until the full process is completed, namely until all the dies are removed from the sticky foil.
This is a limitation for multi-chip die bonding equipment. The bonding process is similar to the process described above, but after the completion of the first die the equipment has to change the wafer because a different die is required for the same package.
Therefore, in such process where it is inherent to load and reload the same wafer several times, the setup process is provided without wafer expansion.
As a consequence the lack of clearance between adjacent dies will induce various pick-up process issues.